After assassinating eight Templars by the command of his Master, Altaïr soon hunted down the ninth, Robert de Sable. After Altaïr struck down Robert at Arsuf, the Templar revealed Al Mualim as the tenth man who found the treasrue and his intentions to use the Apple of Eden to control the minds of those at Masyaf, and Altaïr left to reclaim control of the village.

After killing Robert de Sable at the Battle of Arsuf, Altaïr returned to Masyaf to learn if Robert had been honest in his final words. When Altaïr entered the main gate, he found the town silent, and was soon confronted by a hypnotized man.

Upon questioning him of what had happened, the man only responded with strange ramblings about being led to "see the light", thus Altaïr quickly dismissed him, and continued towards the fortress. As he neared the stronghold, Altaïr noticed that the entire city's population was in the same hypnotic state as the old man, and were even spouting the same odd words as they followed Altaïr to the stronghold on the top of the mountain.

At the foot of the path that led into the fortress, Altaïr encountered a group of fellow Assassins also locked in a trance, and blocking the way. Upon seeing Altaïr, they slowly surrounded him, and drew their swords. Altaïr had no choice but to fight them off, and he swiftly eliminated the first wave.

However a second wave quickly approached, and the battle started to become overwhelming for the lone Assassin. Suddenly, Malik Al-Sayf and a few other Assassins who had not yet been hypnotized by the Piece of Eden's effect ambushed the attackers with throwing knives, forcing them to flee, and saving their Brother.[1]

Altaïr hastily ran to the top of the hill to meet with his saviors. He announced to Malik how Al Mualim had betrayed their Order, to which Malik agreed, and responded that he had also betrayed his Templar allies as well. Malik explained that after Altaïr's departure from Jerusalem, he had returned to Solomon's Temple and discovered Robert's journal filled with revelations regarding the Apple's use to control the Holy Land.

Malik stated that what he had read broke his heart, but also opened his eyes. Altaïr then advised Malik to lead the other free Assassins to distract the thralls in front of the fortress long enough for him to confront Al Mualim. Before departing, Altaïr asked Malik to try and avoid killing the men he would face, as their minds were not their own. Malik assured him that he would not disobey the Creed as their Master had, and left with the others.

Altaïr trekked onward, and arrived at the fortress courtyard to find a large group of hypnotized people standing near the entrance, civilians and Assassins alike. Moving slowly and carefully, making sure not to harm them, Altaïr made his way through the crowd and into the fortress.[1]

Altaïr searched the fortress for his Master, eventually venturing out into the garden behind the fortress, a place known to the Assassins as "Paradise". As he stepped through the door, it slammed shut behind him, and after a few steps, he became immobilized by the power of Al Mualim's Piece of Eden. Al Mualim then mocked Altaïr from the balcony above, though Altaïr only challenged him to face him.

Altaïr fighting the illusions of the nine Templars

Altaïr asked about Al Mualim's intentions, and the Mentor replied he had found "proof" of the Creed - that "nothing was true and everything was permitted." He then used the Apple to disguise several Assassins as the nine targets Altaïr had been sent to slay, who then attacked Altaïr.

However, they were each dispatched by Altaïr, and the guise faded as each one fell. Al Mualim, who had taken the opportunity to enter the garden himself, then bound Altaïr with the Apple again. Al Mualim claimed that he had stood before a thousand men, all superior to Altaïr, but who had fallen by his hand all the same.

There, Al Mualim created several copies of himself through the Apple to aid him, but during the duel, Altaïr was able to use his gift to identify and strike the real Al Mualim with his blade, causing the clones to vanish.[1]

Al Mualim then decided to have a fair duel with Altaïr, but not before giving his former student an explanation. Altaïr claimed that Al Mualim was worse than Robert, as the Master had claimed the Piece of Eden to be evil, despite intending to use it himself. Convinced of his own good intentions, Al Mualim sighed, and replied that there would never be peace so long as men retained free will.

When Altaïr snarled that he had killed the last man to speak as such, Al Mualim sneered that his threats were just empty words. Altaïr then retorted that they were words he would gladly put into action; Al Mualim merely laughed.

When Altaïr asked his Master why he had never used the Apple to enslave his mind like the other Assassins', Al Mualim explained that who Altaïr was and what he did were intertwined too close together, and robbing him of one would deprive him of control over the other, and the other Templars who knew of the Apple had needed to die.

However, Al Mualim admitted that he had attempted to control him once but failed, due to Altaïr's seemingly natural resistance to the illusions conjured by the Apple. Al Mualim went on to explain that many strange and mythical events - Jesus Christ turning water to wine, Moses parting the Red Sea, the influence of the Greek Goddess Eris in starting the Trojan War - were all merely illusions created by the Apple.

Altaïr retorted that the Templars' plan to create a "New World" using the Apple's power was just as much an illusion as the others; but Al Mualim replied that it was no worse than the world around them, where the Saracens and Crusaders slaughtered each other in the name of craven gods that abandoned the world so long ago. Claiming they were already living in an illusion, he only offered a less violent one. Altaïr responded that at least they choose to believe these phantoms; Al Mualim retorted that the occasional convert or heretic would not agree. When Altaïr said it still isn't right, Al Mualim sighed in disappointment, seeing that he abandoned logic and reason and let emotion take control.

Altaïr defeating Al Mualim

Al Mualim finally remarked that they had come to an impasse; he would not yield in his plan, Altaïr would not join him willingly, and he could not compel the Assassin to follow him. Sighing that he would miss Altaïr, Al Mualim ended the Apple's hold on Altaïr, drew his sword, and he and Altaïr engaged in a final duel to the death.

After a long and hard-fought battle, and despite Al Mualim using the Apple's power to weaken Altaïr and cloak his movements around the gardens to regain strength, the student eventually triumphed, and dealt his former Master a fatal blow.[1]

Altaïr, Malik and two other Assassins watching the map projected by the Apple of Eden

As Al Mualim collapsed to the floor, dying in Altaïr's arms, he was shocked by his defeat, proclaiming that the student had not defeated the teacher. Altaïr replied that "Nothing is true; Everything is permitted", which Al Mualim accepted. As the Apple rolled out of Al Mualim's grasp, Altaïr remarked that the old man had been playing with fire by using the Piece of Eden, and should have instead simply destroyed it in the first place.

Al Mualim reasoned that the Apple he had was the only means of creating true peace in the world, and that he could never destroy such a thing. Altaïr claimed that he would, but Al Mualim doubted this statement.

However, as he approached the Apple, Altaïr became mesmerized by it. Al Mualim challenged him to destroy the artifact as he had claimed he would, but Altaïr replied that he was unable to. With his last breath, Al Mualim sneered that he could, but would not, and finally died.

With Al Mualim defeated, Altaïr turned to the Apple which lay on the ground. Suddenly, the Piece of Eden projected a hologram of the world which showed the locations of the other Pieces of Eden. Malik and the other Assassins arrived soon after, joining Altaïr in the fascination of the artifact. Finally, they looked to Altaïr for guidance and leadership, as he was, as of then, the Mentor of the Assassin Order.[1]

As the new Mentor of the Assassin Order, Altaïr began to the write a journal known as the Codex, a journal which would hold the secrets of the Apple which Altaïr had uncovered, including advancements for the Hidden Blade, and new techniques of assassination. This journal would eventually come into the hands of an Assassin from the Renaissance, Ezio Auditore da Firenze.[2]

As for the Templars, after Robert's death, a newGrand Master of the Knight Templars came to power, and eventually prepared to establish a base in Cyprus, and create the Templar Archive to store such artifacts as the Piece of Eden.[3]